1. Field of the Invention
The present invention relates to a solid state image pickup apparatus and, more particularly, to a solid state image pickup apparatus using a photoelectric converting device of the amplifying type for amplifying photoelectrically converted signal charges and generating.
2. Related Background Art
In recent years, in a solid state image pickup apparatus or the like, examination has been made with respect to a photoelectric converting device of the amplifying type for amplifying photoelectrically converted signal charges and generating. As one of such photoelectric converting devices of the amplifying type, there is a solid state image pickup apparatus using a photoelectric converting device (for example, bipolar transistor, MOS transistor, JFET (Junction Field Effect Transistor), SIT (Static Induction Transistor), etc.) which is constructed in a manner such that a unit pixel has a construction similar to that of a transistor and the charges produced by the light irradiation are accumulated in a control electrode region, and an amplified signal is generated from a main electrode region.
FIG. 1 is a circuit constructional diagram of a photoelectric converting section and a signal reading section of a solid state image pickup apparatus using a bipolar type sensor comprising, for example, the bipolar transistor among the above photoelectric converting devices.
In FIG. 1, reference numeral 1 denotes a bipolar type sensor (equivalently, bipolar transistor); 2 a capacitor to control a base potential of the bipolar type sensor 1; and 3 a PMOS transistor to reset the base potential of the bipolar type sensor 1. One unit pixel is constructed by the bipolar type sensor 1, capacitor 2, PMOS transistor 3. Reference numeral 4 denotes a vertical output line; 5 a horizontal drive line; 6 an MOS transistor to reset the vertical output line 4; 7 a capacitor to accumulate an output signal from the pixel; 8 an MOS transistor to transfer an output from the pixel to the capacitor 7; 9 a horizontal output line; 10 an MOS transistor to transfer an output of the capacitor 7 to the horizontal output line 9; 11 an MOS transistor for buffering which is selected by a vertical shift register and is used to apply a drive pulse to the pixel; 12 a preamplifier to generate a sensor output; 13 an input terminal to apply a pulse to a gate of the MOS transistor 6; 14 an input terminal to apply a pulse to a gate of the MOS transistor 8; 15 an input terminal to apply a drive pulse to the MOS transistor 11; and 16 an output terminal.
FIG. 2 is a timing chart for explaining the operations of a photoconductive converting section and a signal reading section.
As shown in FIG. 2, for example, while a pulse .phi..sub.VC which is supplied to the input terminal 13 is maintained at the high level at time t.sub.1, a pulse .phi..sub.T which is supplied to the input terminal 14 is set to the high level and the MOS transistor 8 is turned on. In this state, since the vertical output line 4 is connected to the ground GND through the MOS transistor 6, the capacitor 7 is also reset to the GND.
Subsequently, the pulse .phi..sub.VC is set to the low level at time t.sub.2, the MOS transistor 6 is turned off, and the vertical output line 4 and capacitor 7 are set into a floating state. In this state, when a pulse .phi..sub.R which is supplied to the input terminal 15 is set to the high level at t.sub.3, a base potential of the bipolar type sensor 1 is raised through the capacitor 2. The signal of the potential corresponding to the base potential in a base region in which the light carriers have been accumulated is generated to an emitter.
After the pulses .phi..sub.T, .phi..sub.R, and .phi..sub.VC were respectively set to the low level, middle level, and high level at time t.sub.4, when the pulse .phi..sub.R is set to the low level at time t.sub.5, the PMOS transistor 3 is turned on and the base of the bipolar type sensor 1 is connected to the ground. After that, when the level of the pulse .phi..sub.R is changed to the high level through the middle level for a time interval from t.sub.6 to t.sub.7, a portion between the base and emitter of the sensor 1 is set into a forward biasing state and the base potential decreases by a base current.
When the level of the pulse .phi..sub.R is changed from the high level to the middle level at time t.sub.8 , the base potential drops by the capacitive coupling through the capacitor 2. The portion between the emitter and base is reversely biased and the accumulation of the light carrier is started.
As described above, a series of operations such as reading operation, resetting operation, and starting operation of the accumulation are sequentially executed every line.
According to such a solid state image pickup apparatus, the light carriers accumulated in the base of the bipolar type sensor constructing the pixels can be amplified and read out. Thus, there is an advantage such that the output signal is hardly influenced by noises of the reading circuit system.
It is also possible to construct in a manner such that the amplifying type photoelectric converting device such as a foregoing bipolar type sensor or the like is used and all of the pixels are reset in a lump. The invention can be also applied to a still video or the like.
FIG. 3 is a circuit constructional diagram of the photoelectric converting section and signal reading section of the solid state image pickup apparatus in case of using the foregoing bipolar type sensor. In FIG. 3, the same component elements as those shown in the solid state image pickup apparatus in FIG. 1 are designated by the same reference numerals and only the component elements with different constructions will be explained hereinbelow.
In FIG. 3, reference numeral 50 denotes an MOS transistor to reset the horizontal output line 9; 33 an emitter follower circuit to set a source potential of the PMOS transistor in order to execute the clamping operation of a pixel S (comprising the bipolar type sensor 1, capacitor 2, and PMOS transistor 3); 34 a PMOS transistor to set a base potential of the emitter follower circuit 33; and 35 a terminal to apply a pulse to a gate of the PMOS transistor 34.
The operation of the above solid state image pickup apparatus will now be described hereinbelow.
First, the pulse at the low level is applied to a terminal 35 and the PMOS transistor 34 is turned on, thereby setting an output of the emitter follower circuit 33 to a positive potential. The output of the emitter follower circuit 33 is connected to a source of the PMOS transistor 3 of the pixel S. When the source potential of the PMOS transistor 3 rises so as to be sufficiently higher than a gate potential of the PMOS transistor 3 as the PMOS transistor 3 is sufficiently set into the ON state as much as possible, holes are implanted into the base of the bipolar type sensor 1 of the pixel through the PMOS transistor 3. Subsequently, by applying the pulse at the high level to the terminal 35, the PMOS transistor 34 is turned off and an output of the emitter follower circuit 33 is set into the grounding potential GND. In this instance, by applying the pulse at the high level to the terminal 13, the MOS transistor 6 is turned on and the vertical output line 4 is set into the GND (the processes until now are called a first reset).
In this state, the vertical shift register is subsequently driven and a reset pulse of the pixel is applied to the terminal 15, thereby sequentially resetting to pixels every line. The bases of the bipolar type sensors 1 of all of the pixels are set into a predetermined potential and are reversely biased (the processes until now are called a second reset).
After the accumulating operation of the light carriers was executed, the pulse at the low level is applied to the terminal 13, thereby turning off the MOS transistor 6. A read pulse is applied from the terminal 15 every line selected by the output of the vertical shift register. The signal output is accumulated into the capacitor 7 through the MOS transistor 8. The signal output accumulated in the capacitor 7 is transferred to the horizontal output line 9 through the transferring MOS transistor 10 selected by the horizontal shift register and is outputted from the output terminal 16 via the preamplifier 12.
The first subject according to the present invention will now be described hereinbelow.
In the solid state image pickup apparatus using the amplifying type photoelectric converting device as mentioned above, the operations such as reading operation, resetting operation, and charge accumulating operation are sequentially executed every horizontal line by the vertical shift register. Therefore, when it takes a time to perform the resetting operation and reading operation, a scanning time by the vertical shift register becomes slow. Consequently, there is a large deviation between the start and end times of the accumulation of the charges of one horizontal line and the start and end times of the accumulation of the charges of the next horizontal line. In the reading operation, it takes a predetermined time for the operations to transfer the signal to the capacitor 7 and to read out the accumulated charges therefrom through the preamplifier 12. Therefore, a predetermined time is also required for the scanning operation by the vertical shift register.
Accordingly, in the case where the light such as to be lit on for only about one field period of time is detected and the field image information at that time is obtained, the overlap period of time between the accumulating period of each line and the lighting period of the time differs every line. There is, consequently, a problem such that even if the incident intensity of the turn-on light into the sensor is equal for all of the lines, an amount of signal charges of the turn-on light differs every line.
The second subject according to the invention will now be described.
Since the above conventional solid state image pickup apparatus performs the reverse bias accumulating operation, there is a problem such that a function such that information indicating which maximum amount of light is irradiated to which position upon accumulation of the signal is obtained and which function is often required when a two-dimensional sensor is used as a photometric sensor is not provided for the conventional solid state image pickup apparatus.